This invention relates to a lightweight, resuable shipping pallet made of any moldable material and which, in addition to being nestable, provides improved stacking qualities.
In the past, the most common pallet was made of wood, but as discussed in many prior art patents, wooden pallets suffered many faults, not the least of which was the fact that wooden pallets are heavy, expensive to make and suffer from weather degradation. The pallets made from molded materials, such as thermoplastics, do not suffer from many such faults and numerous various designs and construction types have been patented.
A variety of methods of achieving great strength have been presented in prior art patents. Deluca U.S. Pat. No. 3,140,672 achieves its strength through a cross-ribbed network which interconnects legs while in Leitzel U.S. Pat. No. 3,187,691 a variety of oblique ribs are used to impart strength. In Toot U.S. Pat. No. 3,424,110 a series of ribs defining rectangles which are intersected by radial ribs are thought to provide support while in Lawlor U.S. Pat. No. 3,762,342 the strength has been found through co-equal, opposite and parallel top and bottom cavities, with the cavities on one side being equal in volumetric capacity of the cavities on the opposite side.
There have been many attempts to provide fully nestable trays. The term "nesting" refers to the ability of one pallet to be positioned on top of and within another so that the vertical components of the two pallets are such that the overall height is less than the sum of the height of the individual pallets. In Sullivan U.S. Pat. No. 3,199,468 nesting was achieved by having a plurality of circular frustum legs which fit into each other. In Heimman U.S. Pat. No. 3,524,415 nesting is achieved by having the hollow leg portions tapered so that legs of one tray telescope within the cavity defined by the legs of another tray. Likewise, in Maryonovich U.S. Pat. No. 3,526,195 legs are tapered to permit entry of a leg of an adjacent pallet for nesting purposes.
However, molded pallets are not without their problems. A major disadvantage of most plastic pallets is that they lack adequate stacking properties or, in order to achieve stackability, several different trays would have to be used. The term "stacking," as used in this application, refers to the placement of one shipping container on top of another shipping container so that the bottom pallet of the top container will rest on the upper pallet of the bottom container. Desirably, as little vertical space as possible should be used, the stack must be stable and lateral shifting of one container with respect to another must be prevented. Likewise, each pallet must be capable of supporting the loads placed upon it.
Prior art patents have considered several stacking approaches, but in applicant's opinion such approaches do not adequately solve stability, shifting and support problems. In Heimman U.S. Pat. No. 3,524,415, stacking is accomplished by using a bottom shipping tray of one design and a separate, differently designed, upper shipping lid. When the tray and lid are fastened together around a load, a shipping container is produced. Neither the tray nor the lid is disclosed as being interchangeably usable as either a top or a bottom member of a shipping container. Further, when another shipping is stacked on the top pallet, the weight of the upper container is not supported by reinforcing ribs or feet of the top pallet, but rather by the decking surface of the top pallet, which is a weaker area of support.
Stacking is also discussed in Maryonovich U.S. Pat. No. 3,526,195 and is accomplished by having the various legs, which are located or positioned asymmetrically with regard to the center line of the pallet, fit into sockets which are provided in the decking surface and immediately adjacent the upper portion of each of the legs. With the end of each leg fitting into such sockets, horizontal or lateral shifting of one pallet with respect to the other would be prevented but the supporting member of the stacked pallet has been shifted from the feet or legs to the decking area within each socket.
The supporting member of pallets is normally the foot or leg portion and, as such, each foot is required to have strength sufficient to support a given load. However, when stacking several shipping containers or loads, one on another, the shipping trays or pallets may well have to support the combined weight of several loads. When a pallet is used as a bottom tray for a shipping container, all of the weight of that shipping container, and any shipping containers stacked thereupon, should be borne by the feet of such pallet. Likewise, when the same pallet is inverted and used as the top tray for a shipping container, all of the weight of any shipping containers stacked thereupon should be borne by the feet of the pallet. In a pallet as described by the Maryonovich patent, for instance, the stacked support function shifts to the decking portion within each socket. The deck area forming the end of each socket has not been designed to act as a support member and at the time when the load factor increases, the weight shifts to an area least able to withstand such weight, the decking.